Observations on Reproduction and Phenology in Some Perennial Asters

Abstract

Populations of several perennial Aster species from dif- ferent habitats and a wide geographic range were cloned and compared under uniform environmental conditions in Urbana, Illinois. Differential responses to the changed environment were in part species-dependent, but mostly were a reflection of genetically fixed adaptation of populations to climate and light conditions in their native habitat. The following ob- servations are noteworthy: (1) Perennial asters are outbreeders. (2) Spontaneous seed production is variable and highest in weedy species, e.g., A. pilosus and A. simplex. (3) Several habit forms can be distin- guished, depending on the taxon: (a) a colonial form which reproduces vegetatively by means of stoloniferous rhizomes; (b) a cespitose form or caudiciform plants with short, often cormoid rhizomes, which give rise to distinct clumps; (c) an intermediate form, exemplified by taxa in the section Multiflori, which exhibits cormoid rhizome portions and cespitose clumps interconnected by horizontal strands; (d) caudiciform plants capa- ble of spreading by means of root sprouts, so far found only in A. pilosus. (4) The presence of geographic gradients was confirmed for Aster by a comparison of flowering dates recorded from the place of origin with those observed in the transplants. The phenology of flowering is under genetic control and determined by at least two independent adaptive stimuli which interact with climatic gradients. While the stimulus of flower initiation is primarily governed by photoperiod, the stimulus for bolting and formation of the inflorescence aopears to be determined largely by light intensity in interaction with temperature. (5) For most Aster species, the period from anthesis to maturation of fruit is approxi- mately 1 month. The achenes in some species require stratification but those of many species can be germinated immediately after harvest. In all species examined, seed germination can be forced at any time by rupturing the pericarp and the seed coat.